The list of weak acids which are normally liquid, or marketed in the form of a water solution, is not large. Included are phosphoric acid, acetic acid, lactic acid and formic acid. Because of the nature of many of the applications or uses for these acids, it would be highly desirable or advantageous if they could be marketed in solid form. However, up to the present time, encapsulated liquid acids have not been commercially available. One reason is believed to be that the acids tend to attack most matrices which are available as encapsulating agents.
The Zoller et al U.S. Pat. No. 4,082,677 describes a process for making a dry phosphoric acid composition in which a phosphoric acid solution of 75% or 85% concentration is absorbed onto a carrier such as peanut hulls, rice hulls and beet pulp, and then subjected to drying. This is said to form a powdery product with a burnt or charcoal-like appearance. The process and product disclosed in this patent are remote from the present invention. The product is said to be very hygroscopic, as would be expected. Carriers such as those disclosed are not suitable as encapsulating agents using conventional encapsulating procedures.
The process of the present invention is preferably one of extrusion, as disclosed in Beck U.S. Pat. No. 3,704,137, dated Nov. 28, 1972, assigned to assignee of the present application. The disclosure of this patent is incorporated by reference herein. Briefly, it defines a process for making relatively stable, particulate, essential oil-rich compositions. In the commercial practice of this prior invention, a melt of sucrose and hydrolyzed cereal solids having a selective, restricted dextrose equivalent, is mixed with an essential oil to form an emulsion. The melt is then extruded into cool, aggitated isopropanol to produce solidified, saccharated particulates entrapping the oil inside them while washing off exposed oil. After drying, the product particulates are usually coated with an anti-caking agent. The particulates have many uses. A few, such as for use in flavoring and/or odorizing beverage powders, pastries, and other ultimate products, are listed in the patent.
A similar procedure is disclosed in Swisher U.S. Pat. No. 3,041,180.
In the Beck extrusion process, the blend of sucrose with hydrolyzed cereal solids is necessary since sugar alone has insufficient oil retention capability. Also, sugar at melt temperature necessary for extrusion starts to invert and can produce a sticky, hygroscopic product. This limits the amount of cook that can be applied to the composition prior to extrusion. Hydrolyzed cereal solids alone have no crystalline structure and simply would extrude to a fine powder rather than to an oil-retaining matrix.
In co-pending U.S. patent application Ser. No. 692,486, filed Jan. 18, 1985, assigned to assignee of the present application, there is disclosed an improvement in the aforementioned process of Beck for obtaining increased loadings in extruded encapsulates. This process comprises forming the matrix composition of a starch hydrolyzate (e.g., maltodextrin) in combination with a modified starch which is a derivative of waxy maize. A preferred modified starch is identified as hydrogen, octenylbutanedioate amylodextrin. It has a Chemical Abstract Registry No. 61932-62-5. This material is commercially available from National Starch and Chemical Corp. under the trademart "Capsul". "Capsul" has a known use as an encapsulating agent in spray drying techniques, but has not been used in an extrusion process similar to the one in co-pending U.S. patent application Ser. No. 692,486.
The disclosure of this application is also incorporated by reference herein.
In another copending application, U.S. patent application Ser. No. 403,966, (now abandoned) filed Aug. 2, 1982 and refiled on May 3, 1985 as continuation application U.S. patent application Ser. No. 730,756, also assigned to assignee of the present application, there is disclosed the combination of a hydrolyzed atarch with a slightly water-soluble or slowly water-soluble inorganic salt (in place of all or part of the sucrose) to produce an extruded delayed release encapsulate. An advantage of the invention disclosed in the '756 application is the ability to prepare a product which is sugar-free or low sugar and yet has the attributes of a conventional sugar containing matrix.
Examples of preferred salts are dicalcium phosphate, tricalcium phosphate and sodium hexametaphosphate. In this application, it is theorized that the hydrolyzed starch in the particle matrix, being readily water soluble, allows water to attack the integrity of the particles, to initiate release of an active ingredient, whereas the presence of the less soluble or slowly soluble inorganic salt tends to preserve such integrity a sufficient degree to prolong release.
Prior to U.S. Pat. No. 4,232,047, Sair et al, describes the preparation of a glasseous extrudate to stabilize essential oils from deterioration and loss during storage. In Example 9, the encapsulating agent is Capsul brand dextrin. Liquid acids are not mentioned in the patent.
In European patent application Publication No. 0070719 to Johnson, published Jan. 26, 1983, Capsul is disclosed as a preferred carrier for spray dried encapsulation of volatile liquids. Liquid acids are not mentioned in this publication either.